1. Technical Field
The technical field relates to a structure of a thin film and more particularly to a structure of a thermoelectric film.
2. Background
In a conventional thermoelectric application field, whether a substance is a favorable thermoelectric material is determined mainly by observing a figure of merit (a ZT value) of the substance. The ZT value is relevant to a Seebeck coefficient, electrical conductivity, and a coefficient of thermal conductivity, and these three parameters pose a direct impact on whether a material is characterized by favorable thermoelectric properties and whether the material is applicable in the thermoelectric application field. The greater the ZT value, the more significant the thermoelectric effects, and the relation therebetween may be represented as follows:
  ZT  =                              α          2                ⁢        σ            k        ⁢    T  
Here, α refers to the Seebeck coefficient, σ refers to the electrical conductivity, k refers to the coefficient of thermal conductivity, and T refers to an absolution temperature. It may be observed from the above equation that a favorable thermoelectric material is required to have not only the satisfactory Seebeck coefficient but also the high electrical conductivity and the low coefficient of thermal conductivity.
Among the physical properties of natural materials, electrical conductivity and thermal conductivity often have an interdependent relationship, and therefore it is rather difficult for a material to have both the high electrical conductivity and the low coefficient of thermal conductivity. Therefore, the resultant ZT value cannot be effectively increased. Even though the control of the electrical conductivity and the thermal conductivity of a material is the key to improve the thermoelectric performance of the material, said difficulty can barely be overcome by applying the existing material-related technologies. Moreover, the overall performance of thermoelectric elements is not only affected by the ZT value but also subject to thermal and electrical impedance generated during interface connection, thermal and electrical impedance of electrode materials, and thermal and electrical impedance of substrates.